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Microprocessor-based systems

Course 11 Computer networks

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The need for communication networks

The need for communication (data and program exchange) between computer systems

Shared use of computing resources (computers, storage, peripheral devices)

First networks: DARPA-NET – network for military purposes Academic networks (Americans) CERN – inter-networks

Today: the network is a communication and cooperation

infrastructure for the development of distributed applications

A set of small computers (PCs), plus a network is more powerful than a computer and several terminals

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Classification of networks

Based on the way it is used: Point-to-point networks, dedicated connection

between two devices Broadcasting networks: communication

medium for more equipment Unicast - one recipient Multicast - multiple recipients Broadcast - all network nodes are addressed Anycast – at least one node is addressed

• After stretching area:• Personal Area Networks (PAN)• Local Area Networks (LAN)• Metropolitan Networks (MAN)• Wide Area Networks (WAN)

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Personal area networks (PANs)

Have a stretch of 1-2m Intended for interconnection of

equipment at an individual phone, PDA, headphones, MP3 player, etc..

Examples: Bluetooth, ZigBee Low speed Wireless connectivity in the

frequency of public

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Local Area networks (LAN)

Interconnect equipment in the same building

Belong to some organizations Distances: 10m-1km Speed: 10-100Mbs, 1Gbs Standard protocols:

Ethernet (CSMA / CD), Token Ring, Token Bus

Low error rate Communication medium: twisted pair or

coaxial electrical cable

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Metropolitan area networks

Interconnected local networks in the territory of a locality or region

Can be private or public Example: the metropolitan network of universities

in Cluj Distances: 1-10km Speed: 100kbs-10Mbs-100Mbs Standard protocols:

DQDB (Double Queue Doubel bus), ATM, Frame Relay

Communication medium: fiber optics

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Wide Area Networks (WAN)

allow transfer of information from very large and diverse places

internet = network of networks Distances: thousand miles Protocol: TCP / IP Speed: 100kbs-10Mbs – 100 Mbs Example:

Internet AOL Geant RoEduNet

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Network communication models

the need for a model: to ensure compatibility between equipment and networks, regardless of manufacturer, type, location

ISO-OSI model - Open Systems Interchange

Separating the functions of communication on several layers of abstraction: 7 layers

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The OSI modelEquipment 1 equipment 2

High-level protocols Application Application Presentation Presentation Session Session Transport Transport The communication sub-network Network Network Network Network Data link Data link Data link Data link Physical Physical Physical Physical Low-level protocols (host-router)

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Packaging the message

Useful content

…….

Header

Footer

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Access to the communication services

Each layer offers a set of communication services There are layers with one type of service (in the

Internet the network layer is only IP), or layers with different types of services (e.g. for transport layer: TCP - connection-oriented service and UDP – service with no connection)

Higher layers access lower layer services through access points (service access points)

Two components of the same layer but from different computers communicate as if they are directly connected - logical connection

A communication travels through the entire protocol stack

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The TCP/IP model compared with OSI

OSI model TCP/IP model Aplication Aplication Presentation Session Transport TCP/UDP Network IP Data Link Layer Host-to-network Physical connection

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ATM model Control Utilizator High layers CS ATM Adaptation SAR layer

ATM Layer

TC Physical Layer PMD

Plane Administration

Layer admin.

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Protocol layers Physical layer

Physical layer deals with information transmission at the bit. A physical layer protocol must specify:

the nature of the signals used to encode binary data (eg voltage layers, currents, laser beam, etc..), and acceptance layers

electrical characteristics, mechanical performance and transmission medium (electrical cables, optical, radio)

methods to reduce noise and eliminate the influence of transmission errors type of connectors used

Physical protocol must ensure efficient use of transmission medium, and a transfer rate as large.

Depending on the nature of transmission medium can use different encryption methods and compaction of binary information.

The transmission media used in digital communication are:a. twisted pair cable - is cheap, with the frequency dependent transmission distance, may be

shielded or unshielded (UTP - Unshielded Twisted Pair), twisting the two wires of the cable increases noise immunity.

b. The coaxial cable - is high bandwidth and high noise immunity, transmission distance is relatively large, there are two ways of using: the basic band (one channel / cable) or broadband (multi-channel / cable )

c. optical fiber - is a transmission medium with high performance parameters (high bandwidth, low delay) has full immunity to electromagnetic noise, on a single optical wireless can transmit many channels

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Physical Layer

Communication media: Twisted pair cable

(UTP) Coaxial cable Fiber Optic Radio IR transmission

Topology: Star Ring Bus Tree graph

Star Ring Bus Tree

Graph

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Data Link Layer

Role: Structuring data within packages Providing a secure communication channel Detecting transmission errors

The parity bits, checksum, CRC Types of services:

unconfirmed service without connection confirmed service without connection confirmed the connection-oriented service

Examples: HDLC protocol (High Data Link Control)

SLIP protocol (Serial Line Internet Protocol) Unaltered IP packets for transmission (Internet)

PPP (Point-to-Point Protocol)

01111110 Adresă Control Date SC 01111110 8 biţi 8 biţi 8 biţi >=0 16biţi 8 biţi

Figura 12-5 Formatul unui cadru HDLC

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Access mechanisms to the communication environment (MAC – sub-layer)

Layer used for local area networks where the same medium is shared by multiple nodes

Access control: Centralized Distributed

Classification of access methods

Algorithm Centralized Distributed

Round-Robin Polling Token ring, Token bus

With reservation Central reservation Distributed reservation

With multiple access ----- CSMA/CD (Ethernet)

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Network layer Role: routing messages Solutions:

Circuit switching - phone system Packet Switched

Routing algorithms: The shortest path routing Flooding algorithm (flooding) Flow-based routing Vector-distance routing Hierarchical routing

Network layer on the Internet – IP (Internet protocol) The network is organized around three hierarchical levels: high-speed network that makes up the backbone of the system (backbone) regional networks (Europe, America, Asia, ..) academic networks, government, companies, ISPs, etc..

The IP addresses: 4 bytes, 232 possible addresses – not enough

A 0 N et H o s t 1 .0 .0 .0 -1 2 7 .2 5 5 .2 5 5 .2 5 5 B 1 0 N e tw o rk H o s t 1 2 8 .0 .0 .0 - 1 9 1 .2 5 5 .2 5 5 .2 5 5 C 1 1 0 R e ţe a G a z d ă 1 9 2 .0 .0 .0 - 2 2 3 .2 5 5 .2 5 5 .2 5 5 D 1 1 1 0 M u lt ic a s t a d d re ss 2 2 4 .0 .0 .0 - 2 3 9 .2 5 5 .2 5 5 .2 5 5 E 1 1 1 1 0 R e se rv e d fo r th e fu tu re 2 4 0 .0 .0 .0 -2 4 7 .2 5 5 .2 5 5 .2 5 5

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Transport layer Role: creates a secure channel of communication on an uncertain

environment It makes a logical connection between remote applications (like a

dedicated pipeline for the two applications) Transport layer on the Internet:

TCP – connection-based transport protocol UDP - connectionless transport protocol

Operations performed: reordering messages in order to respect the initial order re-transmits erroneous messages eliminates duplicate messages

It uses the message confirmation technique Packets are numbered to keep track of their order

Connection is done through sockets (Socket) Socket = port + IP address

Ap1

Ap2

Ap n

Ap1

Ap2

ApnInternet

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Other OSI layers

Session Layer: responsible for controlling the sequence of dialogue

between the two applications that communicate with each

handles authentication dialog between partners by checking the access passwords

Presentation Layer: It deals with issues concerning coding-decoding for data

security Application level:

offers various models and communication interfaces for user applications:

- Network virtual terminal (eg TELNET) - File transfer (eg FTP) - Email (eg SMTP) - Remote execution of procedures (RPT) - Network management (eg SNMP) - Web browsing, etc..

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Other Application layer protocols- DNS (Domain Name System) - is a service that allows addressing

messages based on symbolic names, the protocol allows transformation of symbolic names for network addresses (IP addresses)

- NFS (Network File System) - is a mapping service that allows remote file folders in your local directory, this service provides a uniform access to files regardless of their location

- NIS (Network Information System) - is a service providing resource information contained in the network, such applications can be identified, gateway services, etc.., Resembles the "yellow pages" published to identify firms and services they provide

- RPC (Remote Procedure Call) - is a protocol through which applications can be launched remotely or procedures, the Protocol provides the procedures and appeal mechanisms for transmitting call parameters, many network applications are based on an RPC mechanism

- WWW (World Wide Web) - is a distributed information service that allows searching of information through various databases across the network in Internet, information is organized in the form of pages, a page can contain text, pictures, small applications ( applet's) and especially links to other sites containing similar information, search information is through programs of "navigation" (eg Netscape, Internet Explorer, etc.). is writing pages using HTML and protocol HTTP communication is used.